The invention pertains to a composite absorbent structure and method of making a composite absorbent structure. The invention may be useful in a wide variety of absorbent articles such as, for example, bandages, diapers, diaper inserts, pads hemorrhoid pads, surgical pads, adult incontinence pads, incontinence briefs, training pants, sanitary napkins, tampons, surgical dressings, compresses, hospital underpads, water retaining agents for agricultural and forestry applications, freshness retaining agents for produce and the like.
The discovery of polymeric materials that form gels while absorbing fluids has revolutionized the industry of hygienic and medial products as well as other industries in which strongly absorbent articles are needed. Polymers capable of absorbing water in amounts that are tens to hundreds times their own weight are now standardly used in numerous applications. Among the widely used polymers are crosslinked polyacrylates, starch/acrylic acid graft copolymers, ethylene oxide polymers, cellulose derivatives and the like as well as synthetic polymers such as polyvinyl alcohol. The list of polymers and other additives used in this field, including organic and inorganic salts (and odor killers and perfumes), is well known to those familiar with the art of superabsorbent materials.
In spite of the improved fluid holding capabilities of the above-mentioned superabsorbents and significant progress made in improving the physical properties, chemical properties and architecture of absorbent articles, there are still a variety of important unsolved problems encountered in the production, transport, storage and use of such articles.
One of the acute problems in this field is that of xe2x80x9cdustingxe2x80x9d, i.e. the loss of very fine superabsorbent particles in the process of production or shipping of the said articles. Since the superabsorbent material is relatively costly, dusting translates into monetary losses. In addition, this phenomenon leads to a decrease in the efficiency of the absorbent articles since the amount of superabsorbent material is reduced by dusting. Also, the loss of fine particles is not necessarily homogeneous and it thus may give rise to undesired inhomogeneities in the distribution of superabsorbent particles in the product.
Another problem that affects the quality of the absorbent articles is that of xe2x80x9cgel blockingxe2x80x9d. Fine particles tend to coagulate when wet, and they also tend to block capillaries in the web of fibers that disperses (and partly absorbs) the fluid in the product. In addition, the enhanced mobility of fine particles gives rise to inhomogeneities in the distribution of the superabsorbent particles even in the absence of dusting.
Various remedies have been proposed to overcome these problems, such as adding fumed oxides, for example fumed silica or alumina (presumed to be physisorbed on the surfaces of the polymeric particles), in order to decrease the probability for coagulation (cf. e.g. U.S. Pat. No. 3,932,322 in the name of David Duchane); wrapping of the superabsorbent material with a hydrophobic fibrous material (as in U.S. Pat. No. 4,721,647 in the name of Nakanishi et al.) or hydrophilic fibers (as in U.S. Pat. No. 5,489,469 in the name Kobayashi et al.); entangling short fibers with the polymeric particles such that the protruding ends of the fibers promote interaction with the absorbent web in the article thus immobilizing the polymeric particles; embedding the polymeric particles in matrices of fibrous webs (as, e.g., in U.S. Pat. No. 5,147,343 in the name of Kellenberger; or use of interparticle crosslinked aggregates, macroparticles composed of smaller particles of superabsorbent linked together (as, e.g., in U.S. Pat. No. 5,180,622 in the name of Berg et al. or U.S. Pat. No. 5,324,561 in the name of Rezai et al. or in U.S. Pat. No. 5,330,822 in the name of Berg et al.). It is important to notice that while smaller (finer) particles have disadvantages as mentioned above, they have an advantage over large polymeric particles in that the surface areas per volume (or weight) ratio is higher the smaller the particle, and thus their fluid uptake rate is higher. Other ideas put forward in this field include the use of porous polymeric particles (which have internal voids that can communicate with the exterior of the particles. Still other ideas involve the creation of gradients in the degree of capillarity in order to direct the acquired fluid in desired directions. Another idea, proposed in U.S. Pat. No. 4,699,823 in the names of Kellenberg et al., involves the use of gradients in the number density of the superabsorbent particles.
Among the other problems referred to in this field it is important to mention the lateral wicking properties of the absorbent material, the gel strength (under pressure or shear forces) and problems concerning the size and softness of superabsorbent articles and the like. Production problems, such as workability of the materials involved in the process of making the absorbent articles, safety concerns in the production plant as well as safety and comfort of the user are among the other concerns in this field.
It is an object of the invention to overcome many of the above-noted deficiencies in the prior art, and to provide a novel and unobvious composite absorbent structure and method.
In one aspect, an object of the invention is the utilization of granular material enclosed or substantially enclosed in pervious bags (also referred to as pouches or pockets) in conjunction with an absorbent structure.
In another aspect, it is an object of the invention to increase the mechanical strength of an absorbent article by the provision of a pouch or pouches of granular material.
In another aspect, it is an object of the invention to provide additional space for fluid storage when the superabsorbent particles and the fibrous web are saturated by the provision of a pouch or pouches of granular material.
In another aspect, an object of the invention is the provision of pouches of granular material that are capable of rapid absorption of relatively viscous fluids.
In still another aspect, an object of the invention is the provision of an absorbent article that can actually accumulate more fluid when under pressure or shear forces than without these external forces.
In yet another aspect, an object of the invention is the provision of granular particles that are relatively hard so that external forces exerted on collections of such particles cannot decrease the dimensions of the interparticle pores, and hence such forces cannot squeeze fluid out of the pores.
In another aspect, an object of the invention is the utilization of chemically inert grains, made of, e.g., light plastic materials.
In another aspect, it is an object of the invention to minimize the weight of the granular component by incorporating hollow grains in some embodiments.
In another aspect, it is an object of the invention to provide an absorbent article and method that can serve the additional possible purpose of deodorizing the absorbent article.
In another aspect, it is an object of the invention to incorporate a pouch or pouches of granular matter in absorbent articles containing components such as a water insoluble fibrous web and superabsorbent particles.
With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims, and to the several drawings attached herein.